1. Field of The Invention
The present invention relates to an apparatus for measuring the strength of a magnetic field and, more particularly, to an apparatus for measuring a magnetic field distribution by arranging a plurality of magnetoresistive elements made of a superconductor having a weak coupling at the grain boundaries.
2. Description Of The Prior Art
It has been common to use a magnetoresistive effect for the detection and the measurement of a simple magnetic field. The magnetoresistive element is achieved by a shape effect of a semiconductor such as InSb or InAs having a high mobility of electrons or by an orientation effect of a ferro magnetic metal such as Fe-Ni alloy or Co-Ni alloy. Research work has been developing to measure or detect, in a high resolution, a weak magnetic field with a magnetoresistive effect of an oxide superconductive material having a weak coupling at the grain boundaries.
In addition to the above method, an extremely weak magnetic field has been detected with the SQUID method using a Josephson effect. For this purpose the Nb mixed allow alloy has been used and should be cooled by liquid He.
In an apparatus of measuring the distribution of magnetic fields and the magnetic field variation with time by using the elements for measuring the magnetic field mentioned above, it is necessary to have a plurality of elements positioned at a plane area necessary for the magnetic distribution measurement.
When the magnetic field distribution and its variation are measured with the method mentioned above, an individual element of measuring the magnetic field is apt to be bulky in size, and must be provided with a lead wire for supplying the electric current and for measuring voltage. It is accordingly difficult to arrange densely the magnetic elements and to elevate the resolution ability of detecting the magnetic field. In addition, each of magnetic elements must be connected with a detecting circuit and there is consequently a problem, that the apparatus cannot be manufactured of small size and in a low cost.